ABSTRACT Rates of adolescent vaping are increasing rapidly. Current high school student use of electronic vaping products (EVPs) rose from 1.5% in 2011 to 20.8% in 2018 ? an increase from 220,000 to 3.05 million adolescent users. Vaping is associated with respiratory symptoms, and exposure to nicotine can act as a `gateway' to other drug use. Effective, school-based interventions are urgently needed to protect adolescents from initiating or continuing use of EVPs. A recent US Surgeon General's report identified no school or community based prevention program that reduces vaping behaviors among youth. This proposal takes advantage of a state-supported prevention initiative to test the efficacy of Above the Influence of Vaping (ATI- V). ATI-V trains peer nominated 8th-9th grade Peer Leader, and adult advisors. Peer Leaders learn skills and implement school-wide prevention campaigns informed by communication science. Preliminary data show that after training approximately 15% of 8th graders as Peer Leaders, who implemented school-wide campaigns, students who were friends of Peer leader had reduced vaping intentions and vaping behaviors 2nd semester of 8th grade. New York State has provided funds to support schools to implement ATI-V but no funds for efficacy research. With support from New York State and a strong team of investigators, our project has three aims: Aim 1. Efficacy. The primary aim of this study is to determine ATI-V impact in preventing vaping use (past 30 days any vaping, nicotine vaping, and regular use). Using an RCT design, 20 schools will be assigned to (a) immediate ATI-V, or (b) wait-list for ATI-V training after 24 months. Approximately 3,800 8th graders will be enrolled and followed for assessments in fall 8th grade, spring 8th grade, spring 9th grade, and mid-year 10th grade. We will test for which students ATI-V is most effective and in what school contexts (school climate). Aim 2. Mechanism. The second aim of this study to test the hypothesized mechanisms of ATI-V impact. To accomplish this aim we will conduct statistical analyses of a mediation model to determine (a) whether ATI-V improves students' perceptions that vaping is unacceptable to their peers (anti-vaping norms), connections to supportive adults to address EVP concerns, and social influence of non-vaping students; and (b) whether the impact of ATI-V on reduced vaping behavior is mediated by these improvements. Aim 3. Implementation (Exploratory). Our exploratory aim is to identify implementation barriers and facilitators by gathering qualitative data (observations, semi-structured interviews) from staff and students from a subset of high and low implementing schools. The purpose is to identify what implementation strategies and supports are needed for future schools to be successful in implementing ATI-V, if warranted by the study findings. If study hypotheses are supported, this study will provide, to our knowledge, the first evidence of a school-based prevention intervention that reduces adolescent vaping behaviors.